The present invention relates to a process for the preparation of a microgel. The term microgel includes microgels and star polymers.
Microgels are macromolecules which possess a very high molecular weight and yet a low viscosity similar to linear or branched polymers of relatively low molecular weight. Microgels are an intermediate structure between conventional linear or branched polymers such as polyethylene or polycarbonate and networks such as vulcanized natural rubber. The dimensions of microgels are comparable with high molecular weight linear polymers but their internal structure resembles a network.
The properties of microgels make them particularly useful in a wide range of applications such as in additives, in advanced material formulations for foams or fibers, in coating compositions, binders and redispersible latexes. Microgels can also be used to improve the ease of processing and to improve the structural strength and dimensional stability of the final products. A further potential use for microgels is as additives for high impact polymers. Microgels embedded in a matrix of conventional linear polymer can act to stabilize the whole structure by distributing mechanical tension. Microgels are also useful in biological systems and as pharmaceutical carriers.
Care is required in preparing microgels as the multiple double bonds present within these systems can readily undergo intermolecular reactions which can lead to intractable networks. PCT/AU98/00015 discloses a process for microgel preparation involving reacting an alkoxyamine with a crosslinking agent. Procedures such as those described by Okay and Funke in Macromolecules, 1990, 23, 2623-2628, require high purity solvent and reagents as well as an inert atmosphere and are complicated by undesirable side reactions. Despite the unique properties of microgels, the difficulties in preparing them have limited their potential and commercial use.
This invention concerns a new process for preparing microgel(s) employing a wide range of activatable prepolymers. The process of this invention produces a polymer composition of crosslinked component A and soluble components B and C from mono-olefinic and multi-olefinic monomers in the presence of catalyst and initiator. The process comprises:
I) introducing mono-olefinic monomer, catalyst, and initiator into a reactor in the absence of multi-olefinic monomer and producing an activatable prepolymer component B;
II) contacting the product of I) with multi-olefinic monomer to produce components A and C, optionally in the presence of additional initiator, also optionally in the presence of additional mono-olefinic monomer and initiator. The ratio of components A/(B+C) can be controlled by varying the mole ratio of (Component B)/(multi-olefinic monomer) from 0.05/1 up to 5/1, by decreasing said mole ratio to increase the ratio of A/(B+C), and increasing said mole ratio to decrease the ratio of A/(B+C).
Component B is the soluble species made in step I, A is the insoluble species made in Step II and C is the soluble species made in Step II.
The prepolymer, B, will be comprised of an activatable prepolymer. As will be understood by one skilled in the art having this disclosure as guidance, the activatable prepolymer is a polymer that under the conditions of the experiment can reversibly generate propagating radicals. The activatable prepolymer contains a group which is adapted to reversibly cleave from the prepolymer B under activating conditions to provide a reactive propagating radical and so promote living/controlled polymerization.
The term activatable prepolymer includes a polymer containing activated halogen (or pseudohalogen) groups, a polymer terminated with thiocarbonylthio groups (including dithiocarbamate, dithiocarbonate, trithiocarbonate, dithioester groups), a macromonomer (a polymer chain having at least one polymerizably-active functionality per polymer chain).
Methods for Preparing Component B(Step I)
Polymers containing halogen (or pseudohalogen) groups are activatable prepolymers in atom transfer radical polymerization (ATRP). Typical examples of transition metal catalysts for atom transfer radical polymerization include complexes such as CuX/2,2xe2x80x2-bipyridyl derivatives, CuX/Schiff base complexes, CuX/N-alkyl-2-pyridylmethanimine, CuX/tris[2-(dimethylamino)ethyl]amine, CuX/N,N,Nxe2x80x2,Nxe2x80x3,Nxe2x80x3-pentamethyldiethylenetriamine, CuX/tris[(2-pyridyl)methyl]amine, Mn(CO)6, RuXx(PPh3)3, NiX {(Oxe2x80x94Oxe2x80x2xe2x80x94CH2NMe2)2C6H3}, RhX(PPh3)3, NiX2(PPh3)2 and FeX2/P(n-Bu)3 wherein X is halogen or pseudohalogen and preferably chlorine or bromine. An alumoxane Al(OR)3 may be used as a cocatalyst. It is believed that the mechanism of ATRP is described in the following scheme: 
Initially, the transition metal catalyst, M abstracts the halogen atom X from the initiator, an arene or alkane sulfonyl halide, Rxe2x80x94X, to form the oxidized species, Mtn+1X, and the sulfur centered radical Rxe2x80xa2. In the subsequent step, the radical, Rxe2x80xa2, reacts with unsaturated monomer, M, with the formation of the intermediate radical species, R-Mxe2x80xa2. The reaction between Mtn+1X and R-Mxe2x80xa2 results in the product, R-M-X, and regenerates the reduced transition metal species, Mtn, which further reacts with Rxe2x80x94X and promotes a new redox cycle. When polymeric halides, R-Mn-X, are reactive enough toward Mtn and monomer is in excess, a number of atom transfer radical events, i.e., a living/controlled radical polymerization occurs. Further, details of this mechanism are described in the reference: Macromolecules, 1995, 28, 7901. See also Macromolecules,1995,28,7970 and Macromolecules, 1996,29,3665 concerning living/controlled radical polymerization using a combination of an arenesulfonyl chloride or alkane sulfonyl chloride and a transition metal compound.
One part of the polymerization system in the process is an arenesulfonyl halide or an alkanesulfonyl halide of the Formula A1SO2X wherein A1 is an aryl, substituted aryl group, an alkyl group or a substituted alkyl group, and X is chlorine, bromine or iodine. Included within the meaning of arenesulfonyl halide and alkanesulfonyl halide is any adduct, such as a 1:1 adduct, which is a reaction product of an arene- or alkyl-sulfonyl halide and any polymerizable vinyl monomer. In effect, such an adduct is one of the initial products in the polymerization process itself.
Another component of the polymerization process system is a compound containing a lower valent transition metal atom. By this is meant a compound containing at least one transition metal atom that is capable of existing in a higher valent state. Included within the definition of a compound containing a transition metal atom in a lower valent state is a compound or combination of compounds that under the polymerization process conditions can form in situ the desired compound containing a transition metal atom in a lower valent state. In some cases, this can include metal itself (or an alloy or a metal oxide thereof) which can dissolve and/or be solubilized to some extent in the process medium.
Suitable lower valent metals include Cu[I], Ru[I], Ni[II], Re[II], Pd[II], Cu[0], Ni[0], Fe[0], Pd[0], and Rh[II]. The transition metal compound should preferably be at least slightly soluble in the polymerization medium. Optionally, the transition metal compound which is added can be solublized by the addition of a complexing agent such as a 2,2xe2x80x2-bipyridine derivative, for example, 4,4xe2x80x2-di(5-nonyl)-2,2xe2x80x2-bipyridine. The complexing agent should also be chosen such that the transition metal has the appropriate redox potential. Other suitable complexes are listed above. The molar ratio of lower valent transition metal compound:arenesulfonyl halide or alkanesulfonyl halide is not critical, but it is preferred that it be greater than 0.2, more preferably greater than 0.5, especially if a living polymerization is desired. It is also preferred that this ratio not be over 5, and more preferably be less than 2.
Thiocarbonylthio and related transfer agents and reaction conditions for the use of these compounds in producing activatable prepolymers are disclosed in Int. Patent Applications WO 98/01478, WO 99/05099 and WO 99/31144 which are incorporated herein by reference.
Preferred thiocarbonylthio chain transfer agents used to form the activatable prepolymer are represented by Formulas III a-c. 
In Formula IIIa:
Z is selected from the group consisting of hydrogen, chlorine, optionally substituted alkyl, optionally substituted aryl, optionally substituted heterocyclic ring, optionally substituted alkylthio, optionally substituted arylthio, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted amino, optionally substituted alkoxycarbonyl, optionally substituted aryloxycarbonyl, carboxy, optionally substituted acyloxy, optionally substituted aroyloxy, optionally substituted carbamoyl, cyano, dialkyl- or diaryl-phosphonato, dialkyl-phosphinato or diaryl-phosphinato and a polymer chain.
R7 is selected from the group consisting of optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted (saturated, unsaturated or aromatic) carbocyclic ring, optionally substituted (saturated, unsaturated or aromatic) heterocylic ring, optionally substituted alkylthio group, and a polymer chain. R7 is chosen such that it forms a free radical leaving group that can initiate free radical polymerization under the reaction conditions.
In Formula IIIb:
n is an integer greater than 1; R7xe2x80x2is an n-valent moiety derived from R7 as defined in Formula IIla and Z is as defined for Formula IIIa.
In Formula IIIc:
n is an integer greater than 1; R7 is as defined in Formula IIIa; and Zxe2x80x2 is an n valent moiety derived from a species selected from the group consisting of optionally substituted alkyl, optionally substituted aryl and a polymer chain where the connecting moieties are selected from the group consisting of aliphatic carbon, aromatic carbon, oxygen and sulfur.
The substituents for the substituted moieties referred to above for R7, R7xe2x80x2, Z and Zxe2x80x2 are selected from the group consisting of hydroxy, tertiary amino, halogen, cyano, epoxy, carboxylic acid, alkoxy, alkyl having 1-32 carbon atoms, aryl, alkenyl having 2-32 carbon atoms, alkynyl having from 2-32 carbon atoms, saturated carbocyclic rings having 3-14 carbon atoms, unsaturated carbocyclic rings having 4-14 carbon atoms, aromatic carbocyclic rings having 6-14 carbon atoms, saturated heterocyclic rings having 3-14 carbon atoms, unsaturated heterocyclic rings having 4-14 carbon atoms aromatic carbocyclic rings having 4-14 carbon atoms.
By a xe2x80x9cpolymer chainxe2x80x9d referred to above for R7, R7xe2x80x2, Z and Zxe2x80x2 is meant conventional condensation polymers, such as polyesters [for example, polycaprolactone, poly(ethylene terephthalate), poly(lactic acid)], polycarbonates, poly(alkylene oxide)s [for example, poly(ethylene oxide), poly(tetramethylene oxide)], nylons, polyurethanes, or chain polymers such as those formed by coordination polymerization (for example polyethylene, polypropylene), radical polymerization (for example, poly(meth)acrylates and polystyrenics), anionic polymerization (for example, polystyrene, polybutadiene), cationic polymerization (for example, polyisobutylene) and group transfer polymerization (for example, poly(meth)acrylates).
Other multifunctional thiocarbonylthio compounds also can be used.
Another class of polymer component B comprises macromonomers depicted by Formula IV and include those disclosed in Int Pat Appl. WO96/15157 and U.S. Pat No. 5,264,530. Reaction conditions for the use of these compounds in producing activatable prepolymers are also disclosed. Preferably macromonomers contain a maximum of 2 double bonds, more preferably macromonomers contain 1 double bond per polymer chain: 
Macromonomers of this type can be prepared by a number of different methods. Two illustrative methods of preparation are (1) use of catalytic chain transfer agents containing Co(II) or Co(III); and (2) addition-fragmentation polymerization. These methods are discussed by Rizzardo et al. in Macromol. Symp. 1997, 111,1.
X is selected from the group consisting of halogen, optionally substituted aryl, alkoxycarbonyl, optionally substituted aryloxycarbonyl, carboxy, optionally substituted acyloxy, aroyloxy, optionally substituted carbamoyl, and cyano.
P is a oligomer or polymer chain as defined above. P is chosen such that it forms a free radical leaving group that can initiate free radical polymerization under the reaction conditions.
The prepolymer component B comprises one or more monomer units; however, it is particularly preferred that the prepolymer is an oligomer comprising at least 3 monomer units and more preferably at least 5 monomer units. The molecular weight (weight average) of the prepolymer components is preferably at least 1000 and more preferably from about 3,000 to 25,000.
Step II: Preparation of Microgel
When the prepolymer includes at least three monomer units (preferably at least 5), the resulting microgel takes the form of linear arms of prepolymer linked to a crosslinked network forming a core. This type of microgel can conveniently be referred to as a star microgel.
The proportion of components used in the process of the invention will generally depend on the desired properties of the microgel and the intended application. Generally, the microgel is prepared using up to 60 mole percent of crosslinking agent based on moles of polymerizable components. More preferably, the crosslinking agent will comprise up to 50 mole percent of the total of the polymerizable components. Typically, the prepolymer component B will compose from about 0.1 to 95 mole percent of the polymerizable components.
The present invention allows a higher proportion of crosslinking agent than has previously been possible for microgel compositions. Prior art microgels have generally been restricted to using no more than several mole percent of crosslinking agent. The ability to use high concentrations of crosslinking agent enables microgels to be prepared with a high density conferring significant advantages in rheology control. Accordingly, it is preferred that the process of the invention uses at least 0.5 mole percent of crosslinking agent based on total of the polymerizable components and most preferably from 0.5 to 50%.
In the process of the present invention, when the average number of monomeric units in the prepolymer portion of the adduct is less than 5 monomeric units it is particularly preferred that the monomer composition include additional monomer(s) selected from monounsaturated monomers and conjugated diene monomers. As the average number of monomer units in the prepolymer portion of the adduct decreases, the improvement provided by using monomer becomes more significant. When the number of monomeric units in the prepolymer is from 1 to 3, a monounsaturated monomer is typically used.
Typically, the unsaturated monomer is present in up to 80 mole percent based on the total number of moles of the polymerizable components and more preferably from 10 to 80%.
When the number of monomer units present in the prepolymer is less than 5, the adduct is preferably present in an amount of from 5 to 60 mole percent.
Star microgels are preferably prepared using from 50 to 95 mole percent of adduct and up to 45 mole percent of monounsaturated monomer.
The additional monomer(s) used in the process of the invention can be any monounsaturated monomer such as an alkene, acrylate, methacrylate, styrene, an alkylstyrene (for example, vinyltoluene), other styrenic monomers, acrylonitrile, methacrylonitrile, vinyl acetate, vinyl chloride or vinylidene chloride, or a conjugated diene monomer such as butadiene, isoprene, chloroprene, or cyclopentadiene.
The properties of the microgel and its reactivity in subsequent applications is controlled by the choice of monomers and their functional groups. Examples of monomers include C2 to C10 alkenes, alkyl acrylates, alkyl methacrylates, hydroxyalkyl acrylates, hydroxyalkyl methacrylates, haloalkyl acrylates, haloalkyl methacrylates, alkoxyalkyl acrylates, alkoxyalkyl methacrylates, N-substituted or N,N-disubstituted aminoalkyl methacrylates, cycloalkyl acrylates, cycloalkyl methacrylates, phenyl acrylate, phenyl methacrylate, alkylene glycol acrylate, alkylene glycol methacrylate, poly(alkylene glycol) acrylate, poly(alkyleneglycol) methacrylate, acrylamides, methacrylamides, derivatives of acrylamindes and methacrylamides, esters of fumaric acid, maleic acid, maleic acid anhydride, N-vinylcarbazole, N-vinylpyrrolidone, vinylpyridine, benzyl acrylate and benzyl methacrylate.
When the prepolymer is an oligomer, the oligomer can be a homopolymer or a copolymer. When the oligomer is a copolymer, it can be a statistical, an alternating, a gradient, or a block copolymer. The monomers used in preparing the oligomer can include one or more functional groups in addition to the double bond. These additional functional groups are selected to confer the desired polarity or reactivity on the arms of the star type microgel. Examples of additional functional groups include halo, amino, hydroxy, carboxyl, mercapto, substituted amino, silane groups and epoxy. Hydroxyfunctional groups such as in the monomer hydroxyethyl methacrylate are particularly preferred. A monomer which includes the additional functional group or groups can be incorporated as a homopolymer chain or as part of a statistical or block copolymer.
Statistical or gradient copolymers can be prepared by using a mixture of monomers. Block copolymers can be prepared by introducing monomers sequentially to provide a block of the first monomer before the second is introduced.
The multiolefinic compound used in the process of the invention preferably contains two or more carbon-carbon double bonds. Other functional groups such as hydroxyl, carboxyl, ester, amide, amino, substituted amino, mercapto, silane and epoxy or the like can be present if desired. Examples of suitable multi-olefinic compounds include divinylbenzene and derivatives of divinylbenzene and monomers containing two or more acrylate or methacrylate functional groups. Examples of such polyacrylate compounds include polyols substituted with two or more double bonds derived from acrylic or methacrylic acids.
Examples of di- and tri-acrylate compounds include compounds of Formula XI: 
wherein R8 and R9 are independently selected from hydrogen, halogen, C1 to C6 alkyl, preferably methyl, and substituted C1 to C6 alkyl such as C1 to C6 hydroxyalkyl;
Y1 and Y2 are independently selected from NR10 and O where R10 is independently selected from hydrogen and alkyl (preferably methyl) substituted C1 to C6 alkyl (such as C1 to C6 hydroxyalkyl) aryl, and substituted aryl; and
Q is any linking group known in the art. Preferred linking groups include alkylene (preferably of 1 to 12 carbon atoms), a carbocyclic or heterocyclic group, a polyalkylene oxide, polyester or polyurethane chain and wherein the groups can optionally be substituted with one or more substituents selected from halo, hydroxy, tertiary amino, substituted amino, silane, epoxy. Q can also contain acrylate or methacrylate group.
Preferably, Q is alkylene of 1 to 10 carbon atoms or a poly(alkylene oxide) and optionally include a substituent selected from hydroxy, amino, silane, epoxy and acrylate or methacrylate. When one or both of R8 and R9 are substituted alkyl, suitable substituents include hydroxy, halo, amino, substituted amino, thiol, silane and epoxy.
Preferred polyacrylate compounds include trimethylolpropane triacrylate, trimethylol propane trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, alkylene glycol diacrylates, alkylene glycol dimethacrylates, poly(alkylene glycol) dimethacrylates, poly(alkylene glycol) diacrylates, poly(oxyalkylene glycol) dimethacrylates, poly(oxyalkylene glycol) diacrylates, 2-cyanoethyl acrylate, alkylene glycol acrylate or methacrylate, poly(alkylene glycol) acrylate or methacrylate. Specific example of multi-olefinic compounds include divinylbenzene, ethylene glycol dimethacrylate, butanediol dimethacrylate, triethylene glycol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, triethylene glycol diacrylate, pentaerythritol triacrylate, 1,3-butylene glycol diacrylate and ethylene glycol acrylate methacrylate and other polyol acrylates or methacrylates.
Allyl and substituted allyl derivatives, such as esters of acrylic and methacrylic acid, ethers and amines can also be used as multi-olefinic compounds.
Some examples are listed below: 
Where R1xe2x95x90H or alkyl
R2xe2x95x90H or alkyl
R1 and R2 may contain functional groups, ie. hydroxy.
where R3xe2x95x90H or methyl
Allyl Acrylates: 
where R1xe2x95x90R2xe2x95x90H R1xe2x95x90H,R2xe2x95x90CH3 R1xe2x95x90R2xe2x95x90CH3 
Allyl Methacrylates: 
where R1xe2x95x90R2xe2x95x90H R1xe2x95x90H,R2xe2x95x90CH3 R1 xe2x95x90R2xe2x95x90CH3 
Diallyl Ethers: 
Where R1xe2x95x90H or alkyl
R2xe2x95x90H or alkyl
R1 and R2 may contain functional groups, ie. hydroxy.
R1 and R2 can also form unsymmetrical structures